pl. 
Vv 
Fic. 213.—The fresh-water mussel (U/20). 
The uppermost figure represents the bivalve in motion in the mud 
with protruded foot (/.) ; note inhalant and exhalant apertures, 
The middle figure shows the inside of the shell(left valve). The 
lower figure shows the outside (right valve). «#., The umbo; 
Z., the ligament; ¢.4., lateral téeth; @.a., anterior adductor 
mark ; a.7,, mark of protractor of the foot; 4.2. pallial line ; 
~-@., posterior adductor mark ; 4,.~., mark of posterior retractor 
of the foot ;4g., a line of growth; 4., anterior (the blunter 
end); P., posterior; V., ventral. 
ar 
